PB2572: LYMPHOPENIA RATE; A FREE EPIDEMIOLOGICAL BIOMARKER FOR COVID-19 PANDEMIC
Authors: Intissar Helali, Ikbel Ghachem, Malek Kaabar, Mootez Oueslati, Mohamed Yassine Kaabar, Asma Bachali
Journal: HemaSphere (2023)

Topic: 30. Infections in hematology (incl. supportive care/therapy) Background: The SARS-CoV-2 (COVID-19) epidemic is until today undoubtedly the epidemic of the century. Since 2020, the spread of the virus has described several epidemiological waves. The massive screening enables to improve the epidemic knowledge in order to control the epidemiological situation and to elaborate a public health strategy but is very costly particularly for developing countries. That is why it is interesting to look for other indicators of epidemiological surveillance. Yet SARS-CoV-2 (COVID-19) pneumonia is frequently characterized by lymphopenia. Could the lymphopenia rate be used as a marker for epidemiological surveillance? Aims: The aim of this study is to investigate a correlation between the number of deaths of SARS-CoV-2 patients and the lymphopenia rate since the beginning of the epidemic. Methods: We enrolled a retrospective descriptive observational study including all patients who performed a complete blood count (CBC) at the Taher Maamouri University Hospital of Nabeul Tunisia, over a period of 34 months, from March 2020 to December 2022. For the CBCs from the same patients, only one test was considered. The lymphopenia rate was calculated monthly from the number of patients with lymphocytes <1.0 G/L and compared to the total number of monthly SARS-CoV-2 deaths available as open-source data from the Tunisian ministry of health. Results: Over the study period, 80234 patients were included. A total of 13299 lymphopenia were identified (16.48%). Annual lymphopenia rate increased from 9.64% in 2019, before the pandemic, to 17.28% in 2022. The monthly lymphopenia rate in the evaluated pre-epidemic period (2019) is around 10%, and then evolves in a strictly parallel way to the number of deaths recorded from March 2020. Each lethal wave of COVID-19 is associated with a peak of lymphopenia rate as shown in the figure below.The correlation coefficient between the two variables for the whole period studied is 0.511, but between September 2020 and September 2021, the two variables show a very high positive correlation (Pearson correlation coefficient value= 0.958). Summary/Conclusion: The correlation we found is an interesting observation. We chose the number of deaths as the reference epidemiological surveillance marker, as it is among the most reliable markers in the absence of mass screening. Our study shows a strong correlation between the two variables during the covid waves. This correlation is decreased with the herd immunization (generalization of the vaccination and natural immunization) and consequently the decrease of the mortality related to SARS-CoV-2 epidemic. The strength of this work lies in the number of cases evaluated, which was made possible by the computer extraction of the results recorded in the laboratory information system (LIS). It would be interesting to study the correlation between the lymphopenia rate and the number of cases identified, especially after the generalization of the use of the covid rapid tests. This observation may allow retrospective epidemiological investigations when mass screening has not been performed and should be verified in other studies to support the usefulness of using the lymphopenia rate as a low-cost tool for epidemiological evaluation. Keywords: COVID-19, Absolute lymphocyte count, Prediction